Cysteine is nutritionally important for protein synthesis, glutathione formation, and as a precursor of sulfate, taurine, thiosulfate, and other metabolites. Also, glutathione, taurine, and 3 feet -phospho-5 feet -phosphosulfate are all cosubstrates for conjugation reactions involved in the metabolism or detoxification of many drugs and xenobiotics. The long-term objectives of this project are (1) to clarify the roles of various metabolic pathways in cysteine metabolism in mammalian tissues; (2) to determine the changes in cysteine metabolism that occur during development and during aging; (3) to determine the effect of diet composition or nutritional status on cysteine metabolism; and (4) to establish the interrelationships of nutrient supply and metabolism during fetal and postnatal development. Specific aims are (1) to elucidate the pathways and steps involved in the synthesis of taurine from cysteine in mammalian tissues; (2) to determine the changes in taurine levels, synthesis, and excretion (urine) or secretion (bile, milk) in female animals during pregnancy and lactation; (3) to determine the effect of sex on cysteine sulfinate decarboxylase; (4) to investigate the relative roles of dearbosylation and transamination (or oxidative deamination) in the catabolism of cysteine, cysteine sulfinate, and cysteate under dietary or hormonal conditions that influence the activity of cysteine dioxygenase or cysteine sulfinate (cysteate) decarboxylase; and (5) to determine the nature of the apparent dilution or trapping of sulfur from cysteine relative to the carbon of cysteine in body pools. Our knowledge of the metabolic pathways and the control or regulation of flux through these pathways has lagged behind that for most other essential or semiessential amino acids. A continued systematic effort to elucidate the details of cysteine catabolism in mammalian tissues is needed. The metabolism of sulfur-containing amino acids in the developing animal is of particular interest because of the possible nutritional requirement of the fetus and neonate for cysteine, taurine, and other metabolites of cysteine. Both the specific and long-term aims of this project are related to two general areas: (1) an understanding of the pathways of cysteine metabolism and the regulation of these metabolic pathways in the intact mammal and (2) an understanding of sulfur-containing amino acid metabolism and the nutrient requirements for cysteine and taurine during the pre- and postnatal developmental periods.